Linear Drive and Linear Compressor with Adaptive Output

ABSTRACT

An apparatus having at least one of a linear drive having a stator and a rotor configured for reciprocating movement therein along a drive axis between a first and a second rotor reversal point about a rotor zero position, and a linear compressor, having a piston housing and a compressor piston configured for reciprocating movement therein along a piston axis between a first and a second piston reversal point about a piston zero position and configured to be driven by the linear drive, wherein at least one of the rotor zero position and the piston zero position is adjustable.

The invention relates to an apparatus comprising a linear drive, which has a stator and a rotor which is movable in a reciprocating manner therein along a drive axis between a first and a second rotor reversal point about a rotor zero position, and/or comprising a linear compressor which has a piston housing and a compressor piston which is movable in a reciprocating manner therein along a piston axis between a first and a second piston reversal point about a piston zero position and can be driven by the linear drive, and a method for cooling a commodity and/or for compressing a fluid.

Linear compressors are currently being developed for domestic refrigeration equipment, such as refrigerators and/or freezers or air conditioning systems for example. Such compressors are required in different output classes, for example with 7 cooling capacities of 40 W, 70 W, 80 W, 100 W, 120 W, 140 W and 160 W. In this connection the compressors for the different output classes are designed in such a manner that they achieve an optimum efficiency for the respective cooling capacity. With regard to known linear compressors, a special design of linear compressor is required for the individual cooling capacities. Such a design is complex, cost-intensive and considerably increases the spectrum of components and spare parts required.

The object of the present invention is therefore to set down a linear drive and a linear compressor which are comparatively simple to mass produce and which operate reliably and in an energy-saving manner. The object of the invention is also to set down a method for cooling commodities or for compressing a fluid, which can be employed for different cooling capacities and which operates reliably and in an energy-saving manner.

The object is achieved according to the invention by the apparatus and by the method as set down in the independent claims. Further advantageous embodiments and developments, which can each be applied individually or can be combined with one another as desired, are the subject of the respective dependent claims.

The apparatus according to the invention comprising a linear drive, which has a stator and a rotor which is movable in a reciprocating manner therein along a drive axis between a first and a second rotor reversal point about a rotor zero position, and/or comprising a linear compressor which has a piston housing and a compressor piston which is movable in a reciprocating manner therein along a piston axis between a first and a second piston reversal point about a piston zero position and can be driven by the linear drive, makes provision in a first variant such that the rotor zero position or the piston zero position can be adjusted.

The apparatus according to the invention comprising a linear drive, which has a stator and a rotor which is movable in a reciprocating manner therein along a drive axis between a first and a second rotor reversal point about a rotor zero position, and/or comprising a linear compressor which has a piston housing and a compressor piston which is movable in a reciprocating manner therein along a piston axis between a first and a second piston reversal point about a piston zero position and can be driven by the linear drive, makes provision in a second variant such that at least one spring element acts on the rotor or on the compressor piston, the length of which can be varied, in particular shortened.

The apparatus according to the invention comprising a linear drive, which has a stator and a rotor which is movable in a reciprocating manner therein along a drive axis between a first and a second rotor reversal point about a rotor zero position, and/or comprising a linear compressor which has a piston housing and a compressor piston which is movable in a reciprocating manner therein along a piston axis between a first and a second piston reversal point about a piston zero position and can be driven by the linear drive, makes provision in a third variant such that at least one spring element acts on the rotor or on the compressor piston, the spring constant of which can be varied or increased.

The apparatus according to the invention comprising a linear drive, which has a stator and a rotor which is movable in a reciprocating manner therein along a drive axis between a first and a second rotor reversal point about a rotor zero position, and/or comprising a linear compressor which has a piston housing and a compressor piston which is movable in a reciprocating manner therein along a piston axis between a first and a second piston reversal point about a piston zero position and can be driven by the linear drive, makes provision in a fourth variant such that the mechanical power which can be delivered by the linear compressor or by the linear drive can be reduced, in particular from a normalized nominal power value of 1 to 0.6, preferably from a normalized nominal power value of 1 to 0.5, whereby the electromechanical efficiency in the event of a change in the mechanical power is always greater than 60%, in particular greater than 70%, preferably greater than 80%.

The apparatus according to the invention comprising a linear drive, which has a stator and a rotor which is movable in a reciprocating manner therein along a drive axis between a first and a second rotor reversal point about a rotor zero position, and/or comprising a linear compressor which has a piston housing and a compressor piston which is movable in a reciprocating manner therein along a piston axis between a first and a second piston reversal point about a piston zero position and can be driven by the linear drive, makes provision in a fifth variant of the invention such that the electromechanical efficiency falls in the event of a reduction in the mechanical power for a normalized nominal power value of 1 to 0.6 on average with a gradient <0.8, in particular with a gradient <0.5, preferably with a gradient <0.2, by particular preference with a gradient <0.1.

The five variants of the invention exist in parallel, but can also be combined with one another in any manner. With the apparatus according to the invention in the different variants it is possible to build one or two construction types, different in terms of design engineering, of linear drives or of linear compressors which are adjustable in terms of hardware and software such that all output classes above a factor 4 can hereby be covered in the power, for example between 40 W and 160 W. The spectrum of the equipment parts required for coverage of all output classes is considerably reduced in total, as a result of which the costs of a linear compressor are reduced for an individual output class.

The linear drive according to the invention is suited and intended in particular for a linear compressor.

Whereas in the case of known linear drives or linear compressors a varied activation of the linear drive or of the linear compressor required in order to change a cooling capacity would result in a considerable reduction in the electromechanical efficiency, the apparatus according to the invention operates in the specified variants with a high degree of efficiency even in the event of a variation or adaptation of the cooling capacity.

The rotor or the compressor piston executes a reciprocating motion between two respective reversal points, at which the direction of motion changes. In this connection, the rotor or the compressor piston oscillates about a respective zero position. The respective zero positions are predefined by the mechanical oscillation system of the linear drive or of the linear compressor. In the case of a symmetrical design of the linear drive or of the linear compressor, the zero position is situated centrally between the two reversal points.

If a cooling capacity level is changed, the rotor or the compressor piston generally executes a different stroke.

On reducing the cooling capacity of a linear compressor, the amplitude of a piston stroke is reduced for example. In order to operate the linear compressor particularly efficiently, it is advantageous to reduce a dead volume situated in the piston housing. If the linear compressor operates with a smaller piston stroke, then its efficiency is reduced, either as a result of the fact that the dead volume is increased or that the electromechanical motor efficiency is degraded.

It has been recognized that a degradation of the electromechanical motor efficiency on changing the piston stroke and whilst retaining as small a dead volume as possible occurring in the case of known apparatuses has its origin in the fact that at the changed second reversal point a spring is less strongly pretensioned, contains less energy in other words, with the result that any missing spring (energy) needs additionally to be delivered electrically in the compression half-wave. An unequal delivery of electrical energy between compression half-wave and expansion half-wave degrades the electromagnetic efficiency. In addition, further disadvantageous effects can occur: If the second reversal point is increased to the extent that the spring energy at the second reversal point is less than the sum of the spring energy at the first reversal point and the residual gas energy (by virtue of the non-disappearing dead volume at the first reversal point), it is necessary to perform electrical braking during the expansion half-wave. The electrical braking results in a further energy loss and a reduction in the efficiency of the linear compressor or of the linear drive.

As a result of the adaptation of the rotor zero position and as a result of the adaptation of the piston zero position, the mechanical system is adapted to the changed conditions and the linear drive or the linear compressor can continue to operate close to its maximum efficiency in spite of the change in the output class.

The change in the rotor zero position or the piston zero position can be effected by changing the length of a spring element used. Spring elements are understood to include all springs such as for example diaphragm springs or coil springs and also corresponding compound spring packages. By changing the length of the spring element it is possible to shift the piston zero position such that the linear drive or the linear compressor can operate at high efficiency.

By changing the length of the spring element or of the spring constant of the spring element it is however also possible, without changing the rotor zero position or the piston zero position, to shift the natural frequency of the mechanical system in such a marked manner that the linear drive or the linear compressor operates at a correspondingly altered frequency, as a result of which the power of the linear drive or of the linear compressor can likewise be influenced.

Depending on the type of construction of the linear compressor or of the linear drive it can be more advantageous to change the length of the spring element or the spring tension of the spring element. To this end, the spring as such can on the one hand be shortened, in other words the length of the spring in its detensioned state is changed by for example changing the mounting of the spring, but the spring can also be more strongly compressed, as a result of which the length of the spring element changes when installed in the linear compressor or in the linear drive. A change to the spring constant can for example be effected by adding reinforcing elements to the spring. The shortening of the spring can be irreversible, for example by clipping off a part of the spring.

As a result of changing the rotor zero position or the piston zero position and/or as a result of changing the length of the spring element and/or as a result of changing the spring constant of the spring element the linear drive or linear compressor can be operated at its optimum point of sale. By this means it is possible to ensure that the electromechanical efficiency is always greater than 80% in the event of a change in the mechanical power from a normalized nominal power value of 1 to 0.6. The nominal power value for a linear compressor or a linear drive corresponds to the maximum power output provided during continuous operation of the linear compressor or of the linear drive. The mechanical power which can be delivered is based on this nominal power value.

If a linear compressor is designed for example for 32 W, a normalized nominal power value of 0.6 means that the linear compressor is operated at 0.6×32=19.2 W. The electromechanical efficiency is defined by

$\eta_{{el}/{mech}} = \frac{P_{mech}}{P_{mech} + P_{ohm}}$

where P_(mech) is the mechanical power delivered at the linear compressor and P_(ohm) is the ohmic power loss. The electromechanical efficiency thus represented merely approximately reflects the actual electromechanical efficiency because it does not take into consideration the electronics losses for position measurement, processor and drive coil current regulator (MOSFET bridge).

The electromechanical efficiency advantageously falls on reduction of the mechanical power from a normalized nominal power value of 1 to 0.6 on average with a gradient <0.1. Given suitable dimensioning of the spring elements, of the moving masses and the reversal points or zero positions, the electromechanical efficiency can be essentially maintained in spite of the change in the mechanical power delivered by the linear drive or the linear compressor. This stands in contrast to known solutions in which a considerably reduced electromechanical efficiency needed to be accepted if the mechanical power yielded was reduced by more than 10%.

Energy-saving, efficient and reliable operation of the linear drive or of the linear compressor is made possible by means of the invention even in the situation when the power level of the linear drive or of the linear compressor is changed. Through this, the manufacture of a set of different linear compressors or linear drives for different power levels becomes simpler and more cost-effective. With the specified linear compressor or linear drive it is possible to cover all power levels, in particular all cooling capacity classes of linear compressors from 40 W to 160 W, with only two structurally different linear compressors or linear drives. To this end, a linear compressor or a linear drive is designed for a maximum power level, for example a maximum cooling capacity of 160 W, and can be lowered to a half, for example to approx. 80 W cooling capacity, without requiring structural changes to the linear compressor. A second linear compressor or a second linear drive is designed for the maximum cooling capacity of 80 W and can be lowered down to approx. 40 W cooling capacity. Even if such a linear compressor operated beneath the maximum power level is somewhat overdimensioned in respect of its electrical design (for example the drive coils or the drive coil current circuit), the savings effects are advantageous as a result of the drastically reduced diversity and associated with this the increase in product quantities.

In addition, the capability to adapt the zero positions, the spring constants or the spring lengths can also be used in order to fine tune the mechanical oscillation system with regard to the normal manufacturing tolerances, in particular to precisely set the natural frequency. A method for tuning the natural frequency of a linear drive, and/or with a linear compressor, is particularly advantageous.

In one embodiment of the invention a drive coil, which acts with an electromagnetic force on the rotor or on the compressor piston, and a means for controlling the drive coil are provided, whereby the means allows the location of the first rotor reversal point or of the first piston reversal point to be adjusted.

With the aid of this means it is possible on the control side, on the software side for example, to adjust the location of the first rotor reversal point or of the first piston reversal point.

The activation of the drive coil can also take place within the framework of a regulation system in which sensors are provided which sense the position of the rotor or the position of the compressor piston and an appropriate activation of the drive coil is effected on the basis of the position information. The reciprocating motion of the rotor or of the compressor piston can thus be both controlled and also regulated.

In a particularly advantageous embodiment the rotor zero position is adjustable relative to the first rotor reversal point or the piston zero position is adjustable relative to the first piston reversal point in such a manner that the rotor or the compressor piston is able to execute an essentially symmetrical oscillation about the adjusted zero position when the reversal point is changed.

As a result of the adaptation of the zero positions to the respective changed reversal points, the required technical control or regulation motion can be brought into coincidence with the natural motion of the physical oscillation system. A high degree of efficiency of the linear compressor or of the linear drive can be achieved by this means.

As a result of the adaptation of the natural frequency of the mechanical oscillation system, the power delivered can be influenced and the efficiency can be optimized.

In a particularly advantageous embodiment of the invention the rotor and/or the compressor piston are mounted between a spring element on the working side and a spring element situated opposite the latter.

On the working side here means the side on which the work is to be done. In the case of a piston rod, which connects the linear drive to the linear compressor, the working side is the side facing the compressor piston. The opposite side is that facing the rotor. A particularly stable reciprocating motion is brought about by this form of mounting.

In a special embodiment of the invention the spring elements have different spring constants and/or different spring lengths.

The spring elements are advantageously under tension for any position of the rotor or of the compressor piston and in their mounted state have a length which is less than 95% of the uncompressed spring element length, in particular less than 90% of the uncompressed spring element length. This ensures that both spring elements have a tensioning state for each rotor or compressor piston position, which likewise serves to enable a stable reciprocating motion.

In order to avoid any striking it is advantageous for the spring elements to have a length for each position of the rotor or of the compressor piston which is greater than 40% of the uncompressed spring element length, in particular greater than 50% of the uncompressed spring element length. This prevents the spring elements from ever being pressed together to the extent that the individual spring connections come into contact with one another. Any hard striking is effectively avoided by this means.

In a special embodiment of the invention at least one of the following criteria (α1) to (α6) is achieved.

-   -   (α1) the working-side spring element (14) has a spring constant         in the range from 1 N/mm to 5 N/mm, in particular in the range         from 1.8 N/mm to 3.6 N/mm, preferably in the range from 2.3 N/mm         to 2.9 N/mm;     -   (α2) the opposite spring element (15) has a spring constant in         the range from 4 N/mm to 12 N/mm, in particular in the range         from 6.5 N/mm to 9.5 N/mm, preferably in the range from 7.5 N/mm         to 8.5 N/mm;     -   (α3) the working-side spring element (14) has an uncompressed         spring length in the range from 40 mm to 60 mm, in particular in         the range from 48 mm to 62 mm;     -   (α4) the opposite spring element (15) has an uncompressed spring         length in the range from 25 mm to 40 mm, in particular in the         range from 30 mm to 36 mm;     -   (α5) the stroke of the rotor (5) or of the compressor piston (6)         is between 10 mm and 30 mm, in particular between 12 mm and 20         mm;     -   (α6) the first rotor reversal point (11) or the first piston         reversal point (21) can be shifted by at least 5 mm, in         particular by at least 10 mm, preferably by 20 mm.

A combination of the criteria (α1) to (α6) is particularly advantageous, whereby however the individual criteria can each be applied individually or can be combined with one another as desired.

It is furthermore advantageous if the second rotor reversal point and/or the second piston reversal point are fixed. By this means it is possible for example with regard to linear compressors to ensure that the dead volume present in the piston housing is kept as small as possible, which improves the efficiency of the linear compressor.

The apparatus according to the invention can be embodied as a refrigeration device, in particular as a refrigerator and/or freezer or as an air conditioning system.

Although the different variants of the invention have been described separately above, the variants can however also be combined with one another as desired. The variants stand partially overlapping, partially non-overlapping alongside one another.

The method according to the invention for cooling a commodity and/or for compressing a fluid uses the apparatus according to the invention. Commodities can be cooled speedily, reliably and in an energy efficient manner or a fluid can be compressed reliably and efficiently on account of the high efficiency of the linear drive or of the linear compressor, the high reliability and energy economy, even if it is necessary to operate with different power levels.

Further advantageous details and special features will be described in detail with reference to the following drawing which should not restrict the present invention but is intended merely as an illustration by way of example.

In the schematic drawings:

FIG. 1 shows a sectional view of an apparatus according to the invention;

FIG. 2 shows a refrigeration device with an apparatus according to FIG. 1;

FIG. 3 shows a graph in which the electromechanical efficiency of an apparatus according to the invention and also of a known apparatus is plotted against a power output generated therewith.

FIG. 1 shows an apparatus 1 according to the invention in a sectional view with a linear drive 2 and a linear compressor 3. The linear drive 2 has a stator 4, in which a rotor 5 moves in a reciprocating manner along a drive axis 9. The rotor 5 is driven with the aid of a drive coil 16 which is supplied with a drive coil current by a means 17 for actuating the drive coil 16. The rotor 5 oscillates between a first rotor reversal point 11 and a second rotor reversal point 12 and in doing so passes through a rotor zero position 13. The motion of the rotor 5 is sensed with the aid of a position sensor 25 which passes on the position information to the means 17 for actuating the drive coil 16, with the result that in total a control system is implemented for the motion of the rotor 5.

The linear compressor 3 has a piston housing 7, in which a compressor piston 6 oscillates in a reciprocating manner along a piston axis 8 between a first piston reversal point 21 and a second piston reversal point. During its reciprocating motion the compressor piston 6 compresses a fluid 18 which is drawn in by way of a suction connection 18 and is discharged by way of a pressure connection 29. The intake and discharge of the fluid 18 is switched with the aid of a valve plate 30. The compressor piston is mounted in contact-free fashion in the piston housing 7 by means of a housing wall 20 having openings 19. Fluid 18 is forced through the openings 19 by means of a feed system 31 in such a manner that a gas cushion is built up between the housing wall 20 and the compressor piston 6, as a result of which a gas pressure bearing is produced.

The rotor 5 is connected to the compressor piston 6 by way of a piston rod 24 which has two couplings 26 in order to absorb bending forces. The zero positions 13, 23 are defined by the arrangement of spring elements 14, 15. The compressor piston 6 is mounted between a working-side spring element 14 and a spring element 15 situated opposite the latter. The working-side spring element has a length L1 and the opposite spring element 15 has a length L2. The uncompressed spring length of the working-side spring element is 59 mm. The uncompressed spring length of the opposite spring element 15 is 33 mm. The zero positions 13, 23 can be adjusted by means of an adjustment aid 34. The linear compressor operates at a nominal power value of 80 W. If the nominal power value is to be reduced to 40 W, the spring elements 14, 15 are compressed by the adjustment aid 34 and the activation of the drive coils is adapted using the means 17 such that the drive oscillation at the coil 16 coincides approximately with the natural physical motion. By this means, a braking of the linear drive 2 is avoided and a particularly high efficiency is achieved even if the linear compressor 3 is operated at 40 W.

FIG. 2 shows a refrigeration device 10 with an apparatus 1 according to the invention, with which commodities 27 can be cooled speedily, efficiently and in an energy efficient manner. For a product range comprising 7 refrigerators having different power levels from 40 W to 160 W only two different linear compressor designs are required, as a result of which the manufacturing costs of an individual refrigerator are reduced. Thanks to the high efficiency, efficient and energy saving cooling of the commodities 27 is possible.

FIG. 3 shows the electromechanical efficiency of the linear compressor according to the invention (see curve 33) and also the efficiency for a known linear compressor (see curve 32), depending on the respective power delivered by the linear compressors. The electromagnetic efficiency is defined as

$\eta_{{el}/{mech}} = \frac{P_{mech}}{p_{mech} + P_{ohm}}$

The power delivered is normalized to the nominal power, in other words the maximum power achievable during continuous operation of the refrigeration device. It can be seen that with regard to known linear compressors the efficiency essentially depends linearly on the power delivered whereas with regard to the linear compressor according to the invention the electromagnetic efficiency essentially remains constant for delivered power levels of 100% to 50%.

The invention relates to an apparatus 1 comprising a linear drive 2, which has a stator 4 and a rotor 5 which is movable in a reciprocating manner therein along a drive axis 9 between a first 11 and a second 12 rotor reversal point about a rotor zero position 13, and/or comprising a linear compressor 3 which has a piston housing 7 and a compressor piston 6 which is movable in a reciprocating manner therein along a piston axis 8 between a first 21 and a second 22 piston reversal point about a piston zero position 23 and can be driven by the linear drive 2, whereby either the rotor zero position 13 or the piston zero position 23 is adjustable and/or at least one spring element 14, 15 acts on the rotor 5 or on the compressor piston 6, the length of which can be varied, in particular shortened, and/or the spring constant of which can be varied, in particular increased; and a method for cooling commodities 27 and/or for compressing a fluid 18.

The invention is distinguished by the fact that adaptation of the power delivered by the apparatus has no substantial effect on the electromechanical efficiency of the apparatus, as a result of which a linear drive 2 and a linear compressor 3 can be constructed in an especially cost-effective manner since the diversity of the component parts can be considerably reduced.

LIST OF REFERENCE CHARACTERS

-   1 Apparatus -   2 Linear drive -   3 Linear compressor -   4 Stator -   5 Rotor -   6 Compressor piston -   7 Piston housing -   8 Piston axis -   9 Drive axis -   10 Refrigeration device -   11 First rotor reversal point -   12 Second rotor reversal point -   13 Rotor zero position -   14 Working-side spring element -   15 Opposite spring element -   16 Drive coil -   17 Means for actuating the drive coil 16 -   18 Fluid -   19 Openings -   20 Housing wall -   21 First piston reversal point -   22 Second piston reversal point -   23 Piston zero position -   24 Piston rod -   25 Position sensor -   26 Coupling -   27 Commodity -   28 Suction connection -   29 Pressure connection -   30 Valve plate -   31 Feed system -   32 Efficiency without zero position adaptation -   33 Efficiency with zero position adaptation -   34 Adjustment aid -   L1 Length of working-side spring element 14 -   L2 Length of opposite spring element 15 

1-14. (canceled)
 15. An apparatus comprising at least one of a linear drive having a stator and a rotor configured for reciprocating movement therein along a drive axis between a first and a second rotor reversal point about a rotor zero position, and a linear compressor having a piston housing and a compressor piston configured for reciprocating movement therein along a piston axis between a first and a second piston reversal point about a piston zero position and configured to be driven by the linear drive, wherein at least one of the rotor zero position and the piston zero position is adjustable.
 16. An apparatus comprising at least one of a linear drive having a stator and a rotor movable in a reciprocating manner therein along a drive axis between a first and a second rotor reversal point about a rotor zero position, and a linear compressor having a piston housing and a compressor piston configured for reciprocating movement therein along a piston axis between a first and a second piston reversal point about a piston zero position and configured for being driven by the linear drive, the apparatus comprising at least one spring element configured for action on at least one of the rotor and the compressor piston, wherein at least one of the length the spring element can be varied, in particular shortened, and the spring constant of the spring element can be varied, in particular increased.
 17. An apparatus comprising at least one of a linear drive having a stator and a rotor configured for reciprocating movement therein along a drive axis between a first and a second rotor reversal point about a rotor zero position, and a linear reciprocating movement therein along a piston axis between a first and a second piston reversal point about a piston zero position and configured for being driven by the linear drive, the apparatus comprising means for reducing the mechanical power that can be delivered by at least one of the linear compressor and the linear drive, in particular from a normalized nominal power value of about 1 to about 0.6, preferably from a normalized nominal power value of about 1 to about 0.5, whereby at least one of electromechanical efficiency in the event of a change in the mechanical power is always greater than about 60%, in particular greater than about 70%, preferably greater than about 80%, and the electromechanical efficiency falls in the event of a reduction in the mechanical power from a normalized nominal power value of about 1 to about 0.6 on average with a gradient less than about 0.8, in particular with a gradient less than about 0.5, preferably with a gradient less than about 0.2, by particular preference with a gradient less than about 0.1.
 18. The apparatus according to claim 15 and further comprising a drive coil configured for acting with an electromagnetic force on at least one of the rotor and the compressor piston, and means for controlling the drive coil, whereby the means for controlling the drive coil includes means for adjusting at least one of the first rotor reversal point and the first piston reversal point.
 19. The apparatus according to claim 15 wherein at least one of the rotor zero position is adjustable relative to the first rotor reversal point and the piston zero position is adjustable relative to the first piston reversal point in a manner wherein at least one of the rotor and the compressor piston is capable of executing a substantially symmetrical oscillation about the adjusted zero position when the reversal point is changed.
 20. The apparatus according claim 15 wherein at least one of the rotor and the compressor piston are mounted between a spring element on the working side and a spring element disposed oppositely from the working side.
 21. The apparatus according to claim 20 wherein the spring elements are configured with at least one of different spring constants and different spring lengths.
 22. The apparatus according to claim 20 wherein for any position of at least one of the rotor and the compressor piston, the spring elements have a length which is less than about 95% of the uncompressed spring element length, in particular less than about 90% of the uncompressed spring element length.
 23. The apparatus according to claim 20 wherein for any position of at least one of the rotor and the compressor piston, the spring elements have a length which is greater than about 40% of the uncompressed spring element length, in particular greater than about 50% of the uncompressed spring element length.
 24. The apparatus according to claim 20, wherein at least one of: the working-side spring element has a spring constant in the range of about 1 N/mm to about 5 N/mm, in particular in the range from about 1.8 N/mm to about 3.6 N/mm, preferably in the range from about 2.3 N/mm to about 2.9 N/mm; and the opposite spring element has a spring constant in the range from about 4 N/mm to about 12 N/mm, in particular in the range from about 6.5 N/mm to about 9.5 N/mm, preferably in the range from about 7.5 N/mm to about 8.5 N/mm; the working-side spring element has an uncompressed spring length in the range from about 40 mm to about 60 mm, in particular in the range from about 48 mm to about 62 mm; and the opposite spring element has an uncompressed spring length in the range from about 25 mm to about 40 mm, in particular in the range from about 30 mm to about 36 mm; and the stroke of at least one of the rotor and the compressor piston is between about 10 mm and about 30 mm, in particular between about 12 mm and about 20 mm; and at least one of the first rotor reversal point and the first piston reversal point can be shifted by at least about 5 mm, in particular by at least about 10 mm, preferably by about 20 mm.
 25. The apparatus according to claim 15 wherein at least one of the second rotor reversal point and the second piston reversal point is fixed.
 26. The apparatus according to claim 15 wherein the apparatus is at least one of an air conditioning system and a refrigeration device, in particular as at least one of a refrigerator and a freezer.
 27. The apparatus according to claim 15 and further comprising at least one of at least one spring element configured for action on at least one of the rotor and the compressor piston, wherein at least one of the length of the spring element can be varied, in particular shortened, and the spring constant of the spring element can be varied, in particular increased; and means for reducing the mechanical power that can be delivered by at least one of the linear compressor and the linear drive, in particular from a normalized nominal power value of about 1 to about 0.6, preferably from a normalized nominal power value of about 1 to about 0.5, whereby at least one of electromechanical efficiency in the event of a change in the mechanical power is always greater than about 60%, in particular greater than about 70%, preferably greater than about 80%, and the electromechanical efficiency falls in the event of a reduction in the mechanical power from a normalized nominal power value of about 1 to about 0.6 on average with a gradient less than about 0.8, in particular with a gradient less than about 0.5, preferably with a gradient less than about 0.2, by particular preference with a gradient less than about 0.1.
 28. A method for at least one of cooling a commodity and compressing a fluid wherein the method comprises the steps of providing and operating an apparatus including at least one of a linear drive having a stator and a rotor configured for reciprocating movement therein along a drive axis between a first and a second rotor reversal point about a rotor zero position, and a linear compressor having a piston housing and a compressor piston configured for reciprocating movement therein along a piston axis between a first and a second piston reversal point about a piston zero position and configured to be driven by the linear drive, wherein at least one of the rotor zero position and the piston zero position is adjustable. 